You are seeing the output of print Dumper \@sorted; which is a quick way of inspecting the contents of a data structure. Just replace that line with what you had originally.

#print Dumper \@sorted;
open my $fh_out,'>','output.csv' or die "$!";
foreach my $row ( @sorted ) {
  print $fh_out join( ',', @$row ), "\n";
}
close $fh_out;
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